Objective: We hypothesised that patient whose functional tremor (FT) has more “voluntary” aspects may respond better to repetitive transcranial magnetic stimulation (rTMS).

Background: Patients with FT experience their abnormal movements as involuntary. However, FT characteristics suggest its generation partially relies on structures involved in control of voluntary movements. In fact, findings that are incongruent with organic tremors, such as FT frequency entrainment with contralateral voluntary movements, FT amplitude variability with cognitive load or pause of tremor with contralateral ballistic movements all reflect physiological aspects of voluntary movements.  Not all FT patients show these incongruent features, suggesting that mechanisms of FT generation are heterogeneous and that in some cases FT becomes “overtrained” by the central nervous system.

Method: Ten patients with FT underwent 5-day repeated sessions of continuous theta burst stimulation (cTBS) over the motor cortex contralateral to more affected hand. On the first and the last day of stimulation, electromyography and accelerometry of postural tremor was performed, without and with mass loading. Additionally, patients performed battery of tests indicative of FT, including tapping task (3 different frequencies) and cognitive load task (serial sevens), on which basis we calculated FT score for each patient. Response to cTBS was measured objectively as change in tremor amplitude on accelerometry and subjectively. Patients were defined as “responders” if there was a decrease in total power spectrum for at least 40%.

Results: 7/10 patients reported no subjective improvement of tremor. Objectively, 5 patients were responders and 5 non-responders. Responders had higher FT score comparing to non-responders (p= 0,016). There was a significant positive correlation between FT score and reduction of tremor amplitude with cTBS (p = 0,036, rs = -0,700).

Conclusion: Mechanism of cTBS effect on FT in our study could be modulation of motor cortex excitability or placebo effect. More the tremor looks functional/non-organic, more likely it will respond to treatment, possibly as its generations still largely depends on voluntary non-automatic motor network.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/incongruity-of-functional-tremor-predicts-better-response-to-transcranial-magnetic-stimulation-treatment/